This invention is directed to radiography. In particular, it is directed to a radiographic silver halide film that provides improved medical diagnostic images of soft tissues such as in mammography and exhibits improved processing characteristics.
The use of radiation-sensitive silver halide emulsions for medical diagnostic imaging can be traced to Roentgen""s discovery of X-radiation by the inadvertent exposure of a silver halide film. Eastman Kodak Company then introduced its first product specifically that was intended to be exposed by X-radiation in 1913.
In conventional medical diagnostic imaging the object is to obtain an image of a patient""s internal anatomy with as little X-radiation exposure as possible. The fastest imaging speeds are realized by mounting a dual-coated radiographic element between a pair of fluorescent intensifying screens for imagewise exposure. About 5% or less of the exposing X-radiation passing through the patient is adsorbed directly by the latent image forming silver halide emulsion layers within the dual-coated radiographic element. Most of the X-radiation that participates in image formation is absorbed by phosphor particles within the fluorescent screens. This stimulates light emission that is more readily absorbed by the silver halide emulsion layers of the radiographic element.
Examples of radiographic element constructions for medical diagnostic purposes are provided by U.S. Pat. No. 4,425,425 (Abbott et al.) and U.S. Pat. No. 4,425,426 (Abbott et al.), U.S. Pat. No. 4,414,310 (Dickerson), U.S. Pat. No. 4,803,150 (Kelly et al.), U.S. Pat. No. 4,900,652 (Kelly et al.), U.S. Pat. No. 5,252,442 (Tsaur et al.), and Research Disclosure, Vol. 184, August 1979, Item 18431.
While the necessity of limiting patient exposure to high levels of X-radiation was quickly appreciated, the question of patient exposure to even low levels of X-radiation emerged gradually. The separate development of soft tissue radiography, which requires much lower levels of X-radiation, can be illustrated by mammography. The first intensifying screen-film combination (imaging assembly) for mammography was introduced to the public in the early 1970""s. Mammography film generally contains a single silver halide emulsion layer and is exposed by a single intensifying screen, usually interposed between the film and the source of X-radiation. Mammography utilizes low energy X-radiation, that is radiation that is predominantly of an energy level less than 40 keV.
U.S. Pat. No. 6,033,840 (Dickerson) and U.S. Pat. No. 6,037,112 (Dickerson) describe asymmetric imaging elements and processing methods for imaging soft tissue.
In mammography, as in many forms of soft tissue radiography, pathological features sought to be identified are often quite small and not much different in density than surrounding healthy tissue. Thus, mammography is a very difficult task in medical radiography. In addition, microcalcifications must be seen when they are as small as possible to improve detection and treatment of breast cancers. As a result, mammographic films often include relatively high amounts of silver and gelatin to maximize image sharpness when used with a single intensifying screen. The higher amounts of silver and gel may mean that the films are more difficult to process or require longer processing times.
This invention provides a solution to the noted problems with a radiographic silver halide film comprising a support having first and second major surfaces and that is capable of transmitting X-radiation,
the radiographic silver halide film having disposed on the first major support surface, one or more hydrophilic colloid layers including at least one cubic silver halide grain emulsion layer, and on the second major support surface, one or more hydrophilic colloid layers including at least one silver halide emulsion layer,
wherein the cubic silver halide grain emulsion layer comprises cubic silver halide grains comprising from about 1 to about 20 mol % chloride and from about 0.25 to about 1.5 mol % iodide, both based on total silver in the emulsion layer, which cubic silver halide grains have an average ECD of from about 0.65 to about 0.8 xcexcm.
Further, this invention provides a method of providing a black-and-white image comprising exposing a radiographic silver halide film of this invention and processing it, sequentially, with a black-and-white developing composition and a fixing composition, the processing being carried out within 90 seconds, dry-to-dry.
This invention also provides a radiographic imaging assembly comprising a radiographic silver halide film of this invention that is arranged in association with a fluorescent intensifying screen.
The present invention provides a means for providing radiographic images for mammography with a radiographic film that is readily processed using the conventional processing solutions known in the art. In addition, all other desirable sensitometric properties are maintained or improved (such as photographic speed). If desired, the amount of silver used in the films can be reduced without a significant loss in photographic speed.
These advantages are achieved by including certain cubic silver halide grains that are comprised of specific amounts of chloride, iodide, and bromide. The critical amount of iodide provides desired photographic speed and the critical amount of chloride provides desired image tone and rapid processability.